Note: Descriptions are shown in the official language in which they were submitted.
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Clamp assembly for Pipe-laying Vessel and Method of
Laying a Pipeline
Background of the Invention
This invention relates to pipe-laying vessels and to
methods of laying a pipeline. Such vessels and methods are of
particular use in the offshore industry relating to oil and
gas production. The invention relates more particularly to a
clamp assembly on a pipe-laying tower of a pipe-laying
vessel.
One of the tasks that is carried out by certain vessels
in the offshore industry is that of laying pipelines, either
by S-laying or by J-laying.
In 'S" laying, the pipeline leaves the vessel at little
or no inclination to the horizontal, adopts a steeper
inclination in the water and then returns to a generally
horizontal disposition on the seabed. The tension in the
pipeline is often accommodated by a series of track
tensioners mounted along the pipe-laying path, on the vessel.
The track tensioners support the weight of the pipeline and
control passage of the pipeline. S laying is preferred in
shallower water where the natural path of the pipeline is
only ever inclined at a shallow angle as it passes to the
seabed. Examples of S-laying arrangements are shown in WO
2006/085739 and WO 2007/000609.
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In 'J" laying, the pipeline leaves the vessel at a steep
or vertical inclination and the inclination steadily reduces
until the pipeline is in a generally horizontal disposition
on the seabed. J laying often involves moving a new pipeline
section from a substantially horizontal position (along the
deck of the vessel) into a vertical position to align with a
J lay tower mounted on the vessel. A lower end of the new
pipeline section is welded to the upper end of the pipeline,
which is held in place, suspended from the vessel, by a fixed
clamp, located towards the bottom of the J lay tower. Once
the new section of pipeline has been added to the existing
pipeline, the fixed clamp is released and the pipeline
lowered down the J lay tower. During such lowering the
tension in the pipeline may be accommodated by a travelling
block or track tensioners. The upper end of the newly
lengthened pipeline (i.e. the upper end of the new section of
pipeline) is then clamped by the fixed clamp, the travelling
block, if used, is returned to its original position towards
the top of the J lay tower and the process repeated. J-laying
is used primarily for laying pipeline in deep water (that is
typically deeper than 1,000 m). Examples of J-laying
arrangements are shown in WO 2009/153352 and WO 2009/153354.
In the arrangements shown in WO 2009/153352 and WO
2009/153354, a pipestring is brought into a position
alongside a J lay tower on a loading arm and is then
transferred from that position to one aligned with the pipe-
laying path by the clamps on the loading arm. Once the
pipestring is in position on the pipe-laying path, it is
engageable by three line-up clamps which position the
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pipestring in the correct position relative to the end of the
pipeline to which the pipestring is to be joined. An internal
line-up system (referenced 75 in the specifications) is
mounted on the top of the tower structure.
It is an object of the invention to provide an improved
pipe-laying vessel and an improved method of laying a
pipeline.
Summary of the Invention
According to a first aspect of the invention, there is
provided a pipe-laying vessel including a pipe-laying tower
extending upwardly from the vessel, the vessel comprising a
welding station for joining a new pipestring to an end of the
pipeline held by the tower, a clamp assembly on the tower for
engaging a pipestring with a lower end adjacent to the end of
the pipeline held by the tower and with the pipestring
extending upwardly from its lower end alongside the tower,
wherein the clamp assembly comprises a pipestring clamp that
serves both the function of a transfer clamp for transferring
the pipestring from a position alongside the tower but
displaced from the pipe-laying path to a position
approximately aligned with the pipe-laying path, and the
function of a line-up clamp for lining up the pipestring with
the end of the pipeline.
By providing a pipestring clamp that serves both for
transferring a pipestring into a pipe-laying path and for
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lining-up the pipestring, the clamp arrangements can be
simplified and some of the procedures speeded-up.
Preferably, the pipestring clamp is in the region of the
top of the tower. Preferably, the pipestring clamp is for
clamping around an upper end of the pipestring.
Preferably, the pipe-laying vessel also comprises a
separate pipestring elevator for rotating a pipestring from a
substantially horizontal orientation at the base of the tower
to an orientation substantially parallel to the tower.
Preferably, the clamp assembly is mounted not on the
pipestring elevator. Preferably, the clamp assembly, when
serving the function of the transfer clamp, transfers the
pipestring from the pipestring elevator to the position
approximately aligned with the pipe-laying path.
Preferably the pipestring clamp is a friction clamp. The
pipestring clamp is preferably arranged to bear at least the
major part of the weight of the pipestring. In that case it
is especially significant that the same clamp is used for
both transferring and lining-up the pipestring.
Whilst it is within the scope of the invention for there
to he just a single pipestring clamp, there will usually be
several such clamps. The "clamp assembly" according to the
invention is exemplified in an embodiment of the invention
described below by a clamp assembly referred to below as a
"tower clamp assembly" and including a friction clamp as the
pipestring clamp according to the invention. The vessel may
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further include one or more further line-up clamps for lining
up the pipestring with the end of the pipeline. Whilst it is
within the scope of the invention for those further line-up
clamps also to serve the function of transferring the
pipestring into the pipe-laying path, in an embodiment of the
invention described below they do not. In that described
embodiment there are two further line-up clamps and one
further transfer clamp referred to in the embodiment as a
"tower arm" for transferring a pipestring into the pipe-
laying path.
The clamp assembly is preferably mounted on the tower.
The clamp assembly is preferably mounted for pivotal movement
about an axis substantially parallel to the longitudinal axis
of the tower. The assembly may be mounted for movement about
more than axis substantially parallel to the longitudinal
axis of the tower and in a described embodiment of the
invention is mounted for movement about two spaced parallel
axes parallel to the longitudianal axis of the tower. This
provides for a wide range of movements of the assembly in a
horizontal plane.
The clamp assembly is preferably mounted for
translational movement in a direction substantially parallel
to the longitudinal axis of the tower. Preferably, the
translational movement is limited to an upper portion of the
tower. Preferably the translational movement is in addition
to the mounting for pivotal movement and, for example, allows
a pipestring to be lowered from a position above and spaced
from an upper end of a pipeline to which the pipestring is to
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be joined to a position adjacent to the upper end of the
pipeline.
Preferably the orientation of the pipestring clamp is
adjustable. The orientation of the pipestring clamp is
preferably adjustable through pivoting movement about an axis
perpendicular to the longitudinal axis of the tower and, more
preferably the orientation of the pipestring clamp is
adjustable about two mutually perpendicular axes that are
themselves perpendicular to the longitudinal axis of the
tower. Such adjustment may be active or passive; in an
embodiment of the invention described below, the adjustment
is passive, with the orientation of the pipestring clamp
being determined by the other line-up clamps.
The pipestring clamp is preferably also able to rotate
the pipestring about its longitudinal axis. Preferably the
pipestring can be rotated through more than 180 degrees; in
an embodiment of the invention described below, the
pipestring can be rotated through +/- 190 degrees. Preferably
this is an active adjustment. It may be controlled by an
operator lining-up the pipestring held in the pipestring
clamp.
The clamp assembly preferably further includes an
internal line-up clamp arrangement. This enables the internal
line-up clamp arrangement to be in fixed relationship with
the pipestring clamp and therefore automatically aligned with
the pipestring held in the pipestring clamp.
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The internal line-up clamp arrangement preferably
includes an internal line-up clamp garage and an internal
line-up clamp. The internal line-up clamp arrangement
preferably further includes an internal line-up clamp winch
for raising and lowering the internal line-up clamp within
the pipestring. The internal line-up clamp may take any
conventional form.
Preferably the internal line-up clamp arrangement and the
pipestring clamp are adjustably mounted for adjustment as a
unit of their orientation relative to the tower. Preferably
the internal line-up clamp arrangement and the pipestring
clamp are fixed in relation to each other. Preferably the
relative position and orientation of the internal line-up
clamp arrangement and the pipestring clamp are non-
adjustable. This helps to ensure that the internal line-up
clamp arrangement is automatically lined up with a pipestring
held in the clamp assembly.
The vessel may comprise a hang off clamp assembly provided
at a lower region of the tower for clamping pipeline that has
been deployed from the vessel and a travelling clamp with a
travel path along a length of the tower for laying pipeline.
Preferably the pipe-laying tower comprises a first lower
section extending upwardly from a proximal end to a distal
end above the main deck of the vessel, and a second upper
section extending upwardly from the first lower section and
having a length that is at least one third of the length of
the lower section, wherein the travel path of the travelling
clamp is limited to the lower section of the tower. The
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second upper section of the tower may be movably mounted on
the first lower section of the tower, but it is possible for
the first and second sections of the tower to be integral
with one another. The preferred arrangement provides for a
construction in which the upper section of the tower can be
moved in relation to the lower section of the tower
independently of the position of the travelling clamp.
The provision of a pipe-laying tower with upper and lower
sections is described and claimed in UK patent application
no. W02012/101233 entitled "Pipe-laying Vessel and Method of
Laying a Pipeline" with agent's reference "P015336GB", having
the same filing date as the present application. The claims
of the present application may incorporate any of the
features disclosed in that patent application. In particular,
the claims of the present application may be amended to
include features relating to the tower and other associated
features relating to the tower such as the elevator for
conveying a pipestring to a position alongside the tower and
various clamps for engaging different parts of the pipestring
and pipeline. Some of those features are mentioned briefly
below in a description with reference to the drawings.
The tower is preferably of an overall length sufficient
to accommodate two pipe strings end to end. A working station
is preferably provided partway up the tower. It is also
preferred that a working station is provided in the region of
the bottom of the tower. In an embodiment of the invention
described below, there is a working station in the region of
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the bottom of the tower and another working station partway
up the tower. A working station is a station at which the
pipeline being formed can be welded and/or coated and/or
inspected.
In a case where two working stations are provided, they
are preferably spaced apart by the length of a pipestring. It
is then possible for a junction of two pipestrings to be
inspected or worked on at one working station while another
junction is inspected or worked on at another working
station. The working stations are preferably manned.
In a case where the tower comprises a first lower
section and a second upper section, there is preferably a
working station in the region of the top of the first lower
section.
The feature of providing a clamp assembly that also
comprises an internal line-up clamp arrangement is itself a
special and novel feature of the invention. Accordingly, in a
second aspect of the invention there is provided a pipe-
laying vessel including a pipe-laying tower extending
upwardly from the vessel, the vessel comprising:
a welding station for joining a new pipestring to an end
of the pipeline held by the tower,
a plurality of clamps on the tower for holding a new
pipestring with a lower end adjacent to the end of the
pipeline held by the tower and with the pipestring extending
upwardly from its lower end alongside the tower,
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wherein the plurality of clamps includes a pipestring
clamp for clamping around an upper end of the pipestring and
the pipestring clamp is part of a clamp assembly that also
comprises an internal line-up clamp arrangement, the internal
line-up clamp arrangement and the pipestring clamp being
adjustably mounted for adjustment, as a unit, of their
orientation relative to the tower.
Preferably, the pipestring clamp is in the region of the
top of the tower. The pipestring clamp is preferably arranged
to bear at least the major part of the weight of the
pipestring.
Preferably, the pipe-laying vessel also comprises a
separate pipestring elevator for rotating a pipestring from a
substantially horizontal orientation at the base of the tower
to an orientation substantially parallel to the tower.
Preferably, the clamp assembly is mounted not on the
pipestring elevator. Preferably, the clamp assembly, when
serving the function of the transfer clamp, transfers the
pipestring from the pipestring elevator to the position
approximately aligned with the pipe-laying path.
It will be appreciated that all of the features described
above as optional or preferred in respect of the first aspect
of the invention may be employed in the second aspect of the
invention and indeed most of them are employed in an
embodiment of the invention described below.
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Similarly, the feature of providing a pipestring clamp
that is arranged to bear at least the major part of the
weight of the pipestring and that is also able to rotate the
pipestring about its longitudinal axis is itself a special
and novel feature of the invention. Accordingly, in a third
aspect of the invention there is provided a pipe-laying
vessel including a pipe-laying tower extending upwardly from
the vessel, the vessel comprising:
a welding station for joining a new pipestring to an end
of the pipeline held by the tower,
a plurality of clamps on the tower for holding a new
pipestring with a lower end adjacent to the end of the
pipeline held by the tower and with the pipestring extending
upwardly from its lower end alongside the tower,
wherein the plurality of clamps includes a pipestring
clamp in the region of the top of the tower, the pipestring
clamp is arranged to bear at least the major part of the
weight of the pipestring and the pipestring clamp is also
able to rotate the pipestring about its longitudinal axis.
Preferably, the pipestring clamp is for clamping around
an upper end of the pipestring.
Preferably, the pipe-laying vessel also comprises a
separate pipestring elevator for rotating a pipestring from a
substantially horizontal orientation at the base of the tower
to an orientation substantially parallel to the tower.
Preferably, the clamp assembly is mounted not on the
pipestring elevator. Preferably, the clamp assembly, when
serving the function of the transfer clamp, transfers the
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pipestring from the pipestring elevator to the position
approximately aligned with the pipe-laying path.
It will be appreciated that all of the features described
above as optional or preferred in respect of the first aspect
of the invention may be employed in the third aspect of the
invention and indeed most of them are employed in an
embodiment of the invention described below.
The present invention still further provides a method of
laying a pipeline from a pipe-laying vessel, in which the
vessel is in any of the forms described above.
Thus, by way of a first example, the method may include
the step of using a clamp assembly both to transfer a
pipestring from a position alongside the tower but displaced
from the pipe-laying path to a position approximately aligned
with the pipe-laying path and to line up the pipestring with
the end of the pipeline. By way of a second example the
method may include the step of providing an internal line-up
clamp arrangement and a pipestring clamp as a unit and
allowing adjustment of the orientation of the unit relative
to the tower. By way of a third example the method may
include the step of providing a pipestring clamp on the pipe-
laying tower for bearing at least the major part of the
weight of the pipestring and also for rotating the
pipestring.
As should already be understood, features described in
relation to one aspect of the present invention may be
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incorporated into other aspects of the present invention. For
example, the features of the first, second and third aspects
of the invention can all be combined and indeed are combined
in a vessel embodying the invention and described below, and
the method of the invention may incorporate any of the
features described with reference to the apparatus of the
invention and vice versa.
Description of the Drawings
Embodiments of the present invention will now be
described by way of example only with reference to the
accompanying schematic drawings of which:
Figure 1 shows a perspective view of a vessel according
to an embodiment of the invention;
Figure 2a shows a side view of the pipe-laying tower in
an initial state, on the vessel of Figure 1;
Figure 2b shows a front view of the pipe-laying tower,
also in an initial state;
Figure 2c shows a top view of part of the tower, also in
an initial state;
Figure 3 shows a perspective view of the string
elevator, on the deck of the vessel of Figure
1;
Figure 4a shows a perspective view of a tower clamp
assembly;
Figure 4b shows a front view of the tower clamp
assembly;
Figure 4c shows a side view of the tower clamp assembly;
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Figure 4d shows a bottom view of the friction clamp on
the tower clamp assembly;
Figure 5a shows a perspective view of a tower clamp
mechanism; and
Figure 5b shows a perspective view of part of the tower
clamp mechanism.
Detailed Description
Figure 1 shows a pipe-laying vessel 100. The vessel 100
has a bow end 102 and a stern end 101. The bottom of the
vessel, known as the keel line, is labelled as 104. On the
deck 103 of the vessel, at the stern end 101 are various
ramps defining S-laying apparatus 200. Other S laying
apparatus is provided towards the bow of the vessel as more
fully described in W02008/107186. At the stern end 101 is an
S-lay opening 202 to allow the pipeline to enter the water
near the stern of the vessel 100. The vessel 100 also has a
J-laying tower 300 in a middle portion of the vessel partway
along the firing line for S-laying.
Figures 2a and 2b show more detailed views of the J-lay
tower 300 and associated equipment. The tower 300 extends
upwards vertically from the deck 103 of the vessel.
Below the tower is an opening 302 in the hull of the
vessel to the water beneath. This opening allows passage of
the pipeline P from the tower 300 to the water.
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In the following description, the pipeline comprises a
deployed pipeline (where the pipeline in question comprises
pipestrings that have been welded together and substantially
deployed off the vessel 100 below the keel 104 of the vessel
100). This deployed pipeline is labelled as P. The pipeline
also comprises a pipeline that has not been deployed yet and
is still held on the vessel 100. This pipeline comprises a
series of pipestrings PS, P1, P2, P3 which are already or
will be welded together and then deployed in due course.
In particular, PS is the pipestring already welded at
its bottom end to the deployed pipeline P. Hence, pipestring
PS is partly deployed below the keel 104 and partly still on
the vessel 100. P1 is the pipestring welded to the top end of
PS and held in a lower section 310 of the tower, P2 is the
pipestring that is being held in an upper section 311 of the
tower and will be welded to the top of P1 in due course and
P3 is the pipestring currently in a string elevator, which
will be welded to the top of P2 in due course.
Attached to the side of the opening 302 is a flute 320
(sometimes called a J-stinger) which controls orientation of
the pipeline P as it enters the water.
Above the flute 320 and still below the deck 103, is a
hang off clamp assembly 330. The hang off clamp assembly 330
is located close to the flute 320 and just above the sea
water level.
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Above the hang off clamp assembly 330 is a travelling
clamp assembly 340, mounted on two rails 342. The rails 342
extend from above the hang off clamp assembly 330, upwards
through the opening 302, passing through the deck 103 of the
vessel 100 and upwards through the J-lay tower 300 to just
below a welding station 500 located on the tower 300 at about
mid-height.
The travelling clamp assembly 340 comprises a friction
clamp 343 mounted on a trolley 341 on the rails 342. The
trolley 341 comprises four shoes 345 (one at each corner)
which are made up of wheels and act as lateral guides to
guide the travelling clamp assembly 340 up the rails 342. At
the top of each rail is an upper sheave block 344 with a
pulley wheel 346. The travelling clamp assembly 340 can be
moved up and down the rails 342 by the use of cables 347
extending up, over these pulley wheels and attached to the
travelling clamp assembly 340.
The friction clamp 343 is lined up so that it is along
the length of the pipe-laying path or axis 303. The rails 342
extend parallel to this pipe-laying axis 303. The friction
clamp 343 has two front doors (not shown) that can open to
allow a pipestring containing a bulky item to be introduced
into the clamp. In addition, the friction clamp 343 is
mounted to the trolley 341 by means of elastic mounts to
allow an oscillation of +/- 1 degree during bulky item
introduction.
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On the deck 103 of the vessel, to one side of the tower
300 is a coating station 600. The coating station 600 is
mounted on rollers 602 which run on track 601 in the deck 103
to allow the coating station 600 to be moved between a
position adjacent the base of the tower 300 (a working
position) and a position slightly removed from the base of
the tower (a storage position). This allows the travelling
clamp assembly 340 to pass by the coating station 600 and
also allows bulky items to pass by.
The coating station 600 is separate from, and at a
different height to, the welding station 500. This allows a
pipestring to be coated as it passes through the coating
station 600 (i.e. as the pipeline P is being laid by the
travelling clamp assembly 330) after it has been welded to
the pipestring above. The coating and welding steps can take
place independently and in parallel. The coating station 600
can also perform non-destructive tests (NDT) on the pipeline
P and, if necessary, repair or replace any defective welds.
On the other side of the tower 300, is a bulky item
handling skid 700.
Also on that other side of the tower 300 is a string
elevator 400. The string elevator is mounted on rails 405
which extend from the base of the tower 300, along the deck
103 of the vessel so that the string elevator can be
accommodated horizontally on the deck 103 of the vessel. The
rails 405 also extend up substantially the whole length of
that side of the tower 300. The string elevator 400 holds a
pipe-string P3 made up of 3 joints (3J). When the string
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elevator 400 is raised up the tower 300 on the rail 405, the
pipe-string P3 is lined up with a string axis 408, which is
parallel to the pipe-laying axis 303. The string elevator
will be described in more detail in relation to Figure 3.
Various clamps and other laying equipment are located
along the length of the tower 300 as will now be described.
Starting from the top of the tower, there is located a
tower clamp assembly 800, including an articulated friction
line-up clamp 819. The tower clamp assembly 800 is pivotable
so as to move a pipe-string from the string axis 408 to the
pipe-laying axis 303. In Figures 2a and 2b, the tower clamp
assembly is shown clamping a pipestring P2 at one side of the
tower 300 in between the string axis 408 and the pipe-laying
axis 303. The tower clamp assembly BOO will be described in
more detail in relation to Figures 4a to 4c.
A tower arm 371 is located further down the tower, above
the height of the welding station 500. The tower arm 371 is
articulated (with a first and second arm) in the same way as
the friction line-up clamp 819 of the tower clamp assembly
800. Hence, as the friction line-up clamp 819 transfers a top
end of the pipestring P3 from the string axis 408 to the
pipe-laying axis 303, the tower arm 371 is controlled in the
same way to guide a bottom portion of the pipestring P3. This
way the pipestring P3 stays vertical and can be lined up with
the pipe-laying axis 303.
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A tower roller 370 is located about halfway between the
tower clamp assembly 800 and the tower arm 371 and is located
on the pipe-laying axis 303. The tower roller 370 can be
opened or closed around a pipestring P2 on the pipe-laying
axis 303.
A line-up clamp mechanism 352 is provided above the
tower arm 371 and is described in more detail in relation to
Figures 5a and 5b.
The welding station 500 is provided with a roof 502 with
a turntable 503 on the roof 502. The turntable 503 is
provided with a central pipe opening (not shown). Hence, the
turntable allows a weld joint to be provided all the way
round the circumference of the pipe strings.
This station welds the pipestring above it (for example
P2) to the pipestring below it (for example, P1) which, by
then, may be regarded as the upper end of the pipeline P. The
welding station 500 also carries out non-destructive test
(NDT) to check the pipestrings.
A line-up clamp mechanism 353 is provided on the roof
502 of the welding station 500. This line-up clamp mechanism
353 is identical to the line-up clamp mechanism 352 higher up
the tower 300.
The welding station 500 is provided with a safety
balcony 550 extending out from the welding station to under
the string axis 408. The safety balcony 550 prevents the
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pipestring (P2) from falling down, while being transferred
from the string axis 408 to the pipe-laying axis 303.
Underneath the floor 501 of the welding station 500 is
another clamp 372. This clamp 372 acts to keep the pipeline
P, including the previously welded pipestring P1, in the
lower section 310 of the tower in position.
A similar clamp 373 is also provided in the lower
section 310 of the tower. This clamp 373 is located towards
the top of the lower part 312 of the lower section 310 of the
tower. This clamp is mounted on a tiltable base so that it
can be tilted into and out of the pipe-laying axis 303. As
the clamp 372 can be moved out of the pipe-laying axis 303,
this allows for the travelling clamp assembly 340 to travel
up and down on the pipe-laying axis 303 and pass this clamp
373.
Figure 2a also shows a pivoted hydraulic ram 316 that is
used to collapse the tower 300 into transit and bridge-
passage configurations.
Figure 2c shows a plan view of the tower clamp assembly
800 holding a pipestring on the string axis 408. The figure
also shows the position of the pipe-laying axis 303 of the
tower 300.
Figure 3 shows the string elevator 400 at the base of
the tower 300. The string elevator comprises a main beam
structure 409 with three clamps 401, 402, 403 distributed
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along the length of the beam 409. These clamps 401, 402, 403
hold a pipestring P3 on the string elevator. These clamps are
fail-safe and are designed to remain closed in the absence of
hydraulic power, for example. They are also designed not to
open until a pipestring P3 is being gripped by the tower
clamp assembly 800 and tower arm 371, as will be described
later. These clamps are designed to take an axial load of 10%
the weight of the heaviest pipestring to be used.
The string elevator is also provided with a shoe 404 at
a second end furthest away from the tower 300. The shoe 404
provides permanent support for the pipestring P3 while on the
string elevator 400 and is designed to take the weight of the
heaviest pipestring to be used. The main beam structure 409
is mounted at its first end on a locomotion trolley 406. This
locomotion trolley runs up and down the tower 300 on rails
405a. There are also further rails 405b that extend away from
the base of the tower along the deck 103 of the vessel and
provide a guide for a roller provided on the second end of
the string elevator 400. Importantly, the rails 405b are
curved at the region at the base of the tower 300 so as to
provide support for the second end of the string elevator 400
in this region and prevent it getting wedged in the corner at
the base of the tower.
Figures 4a, 4b, 4c and 4d show detailed views of the
tower clamp assembly 800 at the top of the tower 300. The
tower clamp assembly comprises a trolley 801 with rollers 804
on each of its four corners. The rollers 804 are engaged in
two vertical parallel rails 802, to allow the trolley 801 to
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run up and down the rails 802 by +/- 1600mm. A hydraulic
cylinder 803 is connected to the top of the trolley 801 to
control movement of the trolley 801 on the rails 802. The
hydraulic cylinder 803 also acts as a weight compensation
system to accurately control the approach of the pipestring
P2 to the pipeline P to which it is to be joined in the
welding station 500.
A framework 605 is mounted on the trolley 801 so that it
can pivot about a vertical axis. The framework 805 therefore
acts as a first arm extending outwards horizontally from the
trolley 801. The first arm 805 can be rotated with respect to
the trolley 801 by two hydraulic cylinders (not shown). The
framework 805 comprises a vertical end rod at a distal end,
with a secondary arm 809 mounted on it. The secondary arm 809
comprises a sleeve portion which fits over the end rod to
allow the secondary arm 809 to pivot about the vertical end
rod. The secondary arm can be rotated with respect to the
first arm 805 by two rotary actuators 810, 811 mounted on the
end rod at either end of the sleeve.
The pivotally mounted first arm 805 and secondary arm
809 allow the distal end of the secondary arm 809 to be
pivoted from the string axis 408 to the pipe-laying axis 303.
This means that a pipestring P2 held by the tower clamp
assembly 800 (as will be described later) can be transferred
to the pipe-laying axis 303 from the string axis 408. It also
allows the pipestring P2 to be lined up on the pipe-laying
axis 303 with the pipeline P, to which it is to be joined,
beneath it.
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On the distal end of the secondary arm 809, is a
mounting ring 813 with a vertically extending Internal Line-
Up Clamp (ILUC) garage frame 820 within the mounting ring
813. The mounting ring 813 is pivotally mounted on the
secondary arm 809 for pivotal movement about a first
horizontal axis and the garage frame 820 is pivotally mounted
on the mounting ring 813 for pivotal movement about a second
horizontal axis perpendicular to the first horizontal axis.
These two pivotal mountings thus define a Cardan joint
allowing the garage frame 820 to pivot about a vertical axis
In any direction. Pivoting is restricted to about three
degrees by a restraining ring 812 fixed to the secondary arm
809. Furthermore retractable restraints are provided inside
the ring 812, which when not retracted, prevent any pivoting
of the garage frame 820. The garage frame 820 takes the form
of an elongate cage. Within the cage is an ILUC guide 823
(Figure 4b) in the form of an elongate tube extending along
the longitudinal axis of the cage. The guide 823 has a
diameter to correspond to an ILUC 827 contained in the guide
823. The guide 823 is attached to the inside of the cage by a
gimbal joint 826. This gimbal joint 826 allows guide 823 to
pivot slightly within the cage. At the bottom end of the
guide 823 is a bevel protector 824. This bevel protector 824
is installed around the top of the pipestring P2 by 4
hydraulic cylinders 825.
In addition, also at the bottom of the guide 823 are
four radial safety pins 828 that can be moved in and out to
prevent an ILUC 827 from falling through the guide 823. As an
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additional/alternative safety mechanism, safety pins may be
installed at a top end of the ILUC 827 to latch the ILUC on
the top of the guide 823.
Below, the mounting ring 813 is a further ring 814 for
mounting a rotatable friction clamp 819 at the lower end of
the garage frame 820. A still further ring 817 is provided
beneath the ring 014 and a rotatable sleeve 818 is provided
in between the rings 814 and 817. The sleeve 818 can rotate
about the longitudinal axis of the garage frame 820.
Distributed around the circumference of the sleeve 818 are 6
radial cylinders 815 which can be moved radially in and out
with respect to the longitudinal axis. At the inner end of
each cylinder 815 is a friction pad 816. The radial cylinders
815 can move in and out to allow these friction pads 816 to
grip a pipestring P2 and support its weight. As the friction
pads 816 can be moved in and out a variety of pipestring
diameters (from 8 inches to 36 inches diameter) can be
accommodated. As can be seen in Figure 4d, the friction pads
816 are shaped to correspond to the rounded shape of the
outer circumference of the pipestring P2. The sleeve 818 can
be rotated +/- 190 degrees about the longitudinal axis to
allow the pipestring P2 to be rotated to any orientation
about that axis. This allows the gap between bevels and the
out-of roundness between the pipestring P2 and the pipeline P
to which it will be joined, to be balanced out.
The ILUC 827 is connected at its top end to a cable 822
which is wound around an ILUC winch wheel 821. This winch
wheel is mounted at the top of the ILUC garage frame 820. The
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winch wheel 821 can be rotated to deploy and retract the
cable 822, which causes the ILUC to be lowered and raised
through the guide 823. By fully deploying the cable 822, the
ILUC 827 can be lowered down through a pipestring P2 held by
the friction clamp 819 and down to the level of the floor 501
of the welding station 500.
The friction clamp 819 and the ILUC garage frame 820,
are rotatable relative to one another about the axis of the
garage frame but not otherwise adjustable, so that, when the
clamp 819 is clamped to the top of the pipestring P2, the
ILUC garage frame is automatically aligned with the
pipestring P2. Furthermore that alignment is maintained when
the garage frame and friction clamp are allowed to pivot
about a vertical axis during alignment of a pipestring.
The tower clamp assembly 800 also comprises a pre-
heating system (not shown) for induction heating the
pipestring P2.
The clamps 401, 402, 403 on the string elevator 400 and
the friction clamp 819 on the tower clamp assembly 800 are
designed so that they cannot be open at the same time. This
prevents a pipestring P2 from being dropped. This is achieved
by having a mechanical sensor roller (or rollers) on the
tower clamp assembly 800 that detect when the pipestring P2
is clamped in the friction clamp 819. When a pipestring P2 is
held in the friction clamp 819, the mechanical sensor roller
abuts a wheel and operates a valve (or valves). This allows
hydraulic fluid to flow in various flow paths and allow the
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string elevator clamps 401, 402, 403 to open. Importantly, in
the absence of any hydraulic flow (i.e. in a natural state),
the clamps 401, 402, 403 remain closed.
Figures 5a and 5b show a line-up clamp mechanism 352
(the line-up clamp mechanism 353 being of the same design).
The line-up clamp mechanism 352 comprises a truss frame 360
upon which the clamp itself is mounted. The clamp itself
comprises a main body 361 located in the truss structure 360
and two clamp fingers 362 protruding out from the main body
361 outside the truss structure 360.
The outside edge of the main body 361 has an
approximately semi-circular notch to accommodate one half of
a pipestring. The two clamp fingers 362 are pivotally mounted
on the main body 361 so as to be able to rotate inwards
towards each other. Hydraulic cylinders 366 are provided to
actuate the clamp finger 362. Each finger 362 has a curved
inward edge so as to form a circular hole with the main body
361 when in a closed position. A pipestring can be held in
this circular hole. The main body 361 also comprises two
rollers and each finger comprises one roller each at the
curved edges. These four rollers 365 allow a pipestring to be
held by the clamp in a certain horizontal position whilst
still allowing the pipestring to be moved vertically up and
down through the clamp.
Rollers 363 are mounted on the truss frame 360 to allow
the truss frame 360 to move forwards and backwards in
relation to the tower 300. The main body 361 of the clamp is
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also provided with rollers 364 to allow the clamp to be moved
sideways in relation to the truss frame 360.
Laying of a pipeline using the tower 300 will now be
described with particular reference to the operation of the
tower clamp assembly 800, including the ILUC arrangement.
Details of the general operation away from the tower clamp
assembly and the ILUC arrangement are generally not of
relevance to the present invention and are not described
fully here. A more detailed description of them can be found
in UK patent application no. W02012/101233 entitled "Pipe-
laying Vessel and Method of Laying a Pipeline" with agent's
reference "P015336GB", having the same filing date as the
present application.
Figure 2a, which has already been described, shows the
tower 300 and associated equipment in a first state. Here,
pipestring P1 is on the lower section 310 of the tower and is
welded to pipestring PS and the deployed pipeline P.
Pipestring P2 is located on the upper section 311 of the
tower. It is being held by the friction clamp 819 of the
tower clamp assembly 800 and tower arm 371. The ILUC 827 is
partly deployed and is positioned mid-way down the length of
the pipestring P2. As will be appreciated, because the
friction clamp assembly and the ILUC arrangement are one
unit, the insertion of the ILUC into the pipestring P2
requires no lining up of those parts relative to one another.
Pipestring P2 is not held directly above pipestring P1 on the
pipe-laying axis 303. Instead, it is held in a stand-by
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position in between the string axis 408 and the pipe-laying
axis 303. Pipestring P3 is clamped to string elevator 400 on
the deck 103 of the vessel.
In the state shown in Figure 2a, the friction clamp 343
holds the top of the pipestring PS. The hang off clamp 330 is
open. The travelling clamp assembly 340 has just deployed
pipeline after moving from the top of its travel path to the
bottom of its travel path, as shown in Figure 2a. The line-up
clamp mechanisms 352 and 353 are open and the friction clamp
819 is closed and holding the weight of the pipestring P2,
while the tower arm 371 retains a lower part of the
pipestring P2 in position.
The hang off clamp 330 is then closed around pipestring
PS to take the weight of the deployed pipeline P below it.
Once the hang off clamp is taking this weight, the friction
clamp 343 is released from PS. The first 805 and secondary
809 arms of the tower clamp assembly 800 (and the
corresponding tower arm 371) are rotated to bring pipestring
P2 onto the pipe-laying axis 303.
The ILUC 827 is lowered further down pipestring P2 to
the join of pipestrings P2 and Pl. Line-up clamp mechanisms
352, 353 and tower roller 370 are closed around pipestring
P2. The tower arm 371 is then released from pipestring P2 and
rotated back to the stand-by position.
Line-up is performed using line-up clamp mechanisms 352,
353. Friction clamp 819 and tower roller 370 follow the
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movement of the pipestring P2 and are "slave" line-up
devices. If necessary, friction clamp 819 is rotated to match
the off-roundness of the upper end of pipestring P1 with the
lower end of pipestring P2. This line-up operation is
performed by welding station 500 operators using a hand-held
portable console.
Welding of pipestrings P1 and P2 is then performed in
the welding station 500, with the ILUC 827 in position inside
the pipeline at the junction of the pipestrings P1 and P2.
Also the pipestring P1 may be coated or otherwise treated in
the coating station 600.
Once welding of pipestrings P1 and P2 is complete, the
ILUC is raised up through pipestring P2 to the garage frame
820. The tower roller 370 is energised so that the pipestring
P2 can be held in position. The friction clamp 819 is then
released and the first 805 and secondary 809 arms of the
tower clamp assembly 800 are rotated so that the friction
clamp 819 is rotated to the stand-by position. The clamp 373
is folded into its stand-by position and the travelling clamp
assembly 340 is raised past the clamp 373 towards the top of
its travel path.
Friction clamp 819 and tower arm 371 are then moved from
the stand-by position and closed around the next pipestring
P3 which has by then been raised on the string elevator 400
and the string elevator clamps 401, 402, 403 are released.
The first 805 and secondary 809 arms of the tower clamp
assembly 800 (and the tower arm 371) are then rotated to
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bring pipestring 33 into the stand-by position above the
safety balcony 550. The ILUC 827 is lowered through
pipestring P3 to about mid-way along its length. When the
travelling clamp assembly 340 has reached the top of its
travel path just below the welding station 500, it is clamped
around the top region of the pipestring Pl. The travelling
clamp assembly 340 then takes the weight of the deployed
pipeline P and pipestrings PS and Pl. The hang-off clamp is
then released and the travelling clamp assembly 340 is
lowered to deploy pipeline. It is lowered to the bottom of
its travel path (as in Figure 2a). This pulls pipestring P1
into the position occupied by pipestring PS in Figure 2a. It
also pulls down pipestring P2 to the position occupied by
pipestring P1 in Figure 2a. The line up clamp mechanisms 352
and 353 are released and other parts are also then returned
to the first state of Figure 2a again, ready to deploy
another pipestring of pipeline.
It can be seen that in this embodiment of the invention,
the top section of the tower 311 is used for receiving the
pipestring P3 from the string elevator 400 and for line-up of
the pipe-string on the pipe-laying path 303. The bottom
section of the tower 310 is used for welding the pipestrings
P3, P2, P1 and the pipeline P together and lowering the
joined pipeline P from the top of the bottom section 310
using the travelling clamp assembly 340.
Whilst the present invention has been described and
illustrated with reference to a particular embodiment, it
will be appreciated by those of ordinary skill in the art
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that the invention lends itself to many different variations
not specifically illustrated herein.
For example, the embodiment described above is designed
for use in laying pipestring formed from 3 joints (3J). In
other words, each pipestring is made up of 3 lengths of pipe,
welded or pre-fabricated together in some way. This pre-
fabrication usually takes place on the vessel. A typical 3J
pipestring will be approximately 37.5m long. However, other
embodiments may be designed for laying 1J, 2J, 4J, or more.
As will be understood, a 1J pipestring consists of a single
length of pipe.
Where in the foregoing description, integers or elements
are mentioned which have known, obvious or foreseeable
equivalents, then such equivalents are herein incorporated as
if individually set forth. Reference should be made to the
claims for determining the true scope of the present
invention, which should be construed so as to encompass any
such equivalents. It will also be appreciated by the reader
that integers or features of the invention that are described
as preferable, advantageous, convenient or the like are
optional and do not limit the scope of the independent
claims. Moreover, it is to be understood that such optional
integers or features, whilst of possible benefit in some
embodiments of the invention, may not be desirable, and may
therefore be absent, in other embodiments.
